Gateless injection mold for encapsulating semiconductor devices

ABSTRACT

In the step of plastic encapsulation of a semiconductive device, the inner ends of a group of leads comprising part of a lead frame, the semiconductive chip and the connections between the chip and the inner ends of the leads, are put into a cavity of a mold and fluid encapsulating material is forced into the cavity to surround the elements that are in the cavity with encapsulating material. A lead frame, which may be supplied in strip form, is provided, a part of which is so formed as to act as a gate for the admission of fluid encapsulating material into the mold cavity.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 388,620, filed June 11,1973 and now abandoned, which in turn was a division of Ser. No. 79,601,filed Oct. 9, 1970, and now U.S. Pat. No. 3,753,634.

RELATED INVENTIONS

The invention of the present application is related to those in thefollowing patents assigned to applicants' assignee; U.S. Pat. No.3,444,441, issued May 13, 1969; U.S. Pat. No. 3,413,713, issued Dec. 3,1968; and U.S. Pat. No. 3,539,675, issued Nov. 10, 1970.

BACKGROUND

It is known to provide lead frames in strip form and to connect bondingpads on a chip on which a circuit has been deposited to inner ends ofcorresponding leads of the lead frame, and then to place the chip, theinner ends of the lead frame and the connections thereto into themolding cavity and to force fluid encapsulating material into the moldcavity, thereby filling the cavity and encapsulating the chip, the innerends of the lead frame and the connections thereto. In doing this inaccordance with the prior art, a gateway in the mold is provided for thecavity for the entry thereinto of fluid encapsulating material and thegateway is connected by a feed runner to a main runner. The main runneris connected to a reservoir into which the encapsulating material isplaced and liquified by applying heat thereto and a piston is forcedinto the reservoir to force the fluid through the main runner, throughthe feed runners and through the gates into the several cavities formedin the mold. The provision of the feed runners and gates complicates theconstruction and maintenance of the mold. Furthermore, in the prior artthe main runner runs alongside the strip frame and to one side thereofwhereby the feed runners are quite long since each thereof runs abouthalf-way across the lead frame from the main runner to the cavities.Each time a mold is used, the cavities thereof and the main and feedrunners must be cleaned out, since a clogged runner will prevent thecavity from being filled with encapsulating fluid, resulting in areduced yield of properly encapsulated semiconductor devices.

It is an object of this invention to provide a lead frame, which may beprovided in the form of a strip of lead frames, which do not requirefeed runners or gates in the mold when the inner ends of the lead framesare encapsulated as part of an encapsulated semiconductor device.

It is another object of this invention to provide the combination of alead strip and a mold requiring no feeder runners or gates in the mold.

SUMMARY

A lead frame is provided which is cut, stamped, etched or formed in anymanner out of conductive material in which at least one of the supportbars, which are integral with the leads near the inner ends thereof, ismade relatively wide so that it can act as at least a portion of thefloor of a main runner for encapsulating material. The wide support baris so notched or formed along the length thereof so that the main leadercommunicates with the space around the chip and its connections thatwill be filled with encapsulating material whereby no feeder runner orgate is required.

DESCRIPTION

The invention will be better understood upon reading the followingdescription in connection with the accompanying drawing in which

FIG. 1 illustrates the lead frame and the mold of this invention intheir cooperative position,

FIG. 2 is a view of the device of FIG. 1 taken on the line 2 -- 2thereof, and

FIG. 3 shows a completed encapsulated device made by use of the leadframe and mold of FIGS. 1 and 2.

A strip 10 of lead frames 12 is provided. While only three lead frames12 are shown in strip form, there may be as many lead frames 12 asdesired in the strip 10. The strip 10 may be made of any suitableconductive material, such as mild steel which is gold plated. While aframe having six leads, three of which come in in opposite directionsfrom the other three, will be described, the frame may be provided withany number of leads and in whatever arrangement thereof that isconvenient.

The strip 10 comprises two end bars 14 and 16 having indexing holes 18along the length thereof. The end bar 14 may also be formed withexternal segmental notches 20 and internal segmental notches 22, whichmay also be used for indexing. Crossbars 24 are provided which runparallel to each other and perpendicularly to the end bars 14 and 16 andwhich include a lead frame 12 between them. The crossbars 24 are sospaced that their facing edges are separated by one dimension, the widthdimension for example of the completed encapsulated semiconductor deviceof FIG. 3, as will be further explained. Each lead frame 12 includes twosupport bars 26 and 28. The bar 26 may be narrow and uniform in widthand extend along the length of the strip 10, being integrally connectedto the crossbars 24. The support bar 28 is quite wide and it alsoextends along the length of the strip 10 and is integral with thecrossbars 24. The facing edges of the support bars 26 and 28 areseparated by another dimension, the length dimension, for example, ofthe encapsulated semiconductor device of FIG. 3. However, the supportbar 28 is not uniform in width in that a notch 30 is formed in the bar28 along the length thereof between two crossbars 24 and facing theother support bar 26. As shown, the notch 30 is between the inner endsof the two leads 32 and 34 that extend towards the crossbar 26 from thecrossbar 28. Also as shown, the inner end of another lead 36 alsoextends from the crossbar 28 towards the crossbar 26. The lead end 32extends nearly perpendicular to the bar 28 and the lead ends 34 and 36curve towards each other so that the ends of the leads 32, 34 and 36,which may be shaped in any convenient shape, are near a chip support pad38. In many types of lead frames, no chip support pad need be provided.It will be understood that the notch 30 can take any shape or dimensionor position as long as it performs its function of acting as a moldinggate, as will be further explained, and as many notches 30 as isdesirable may be used.

The ends of three other leads, 40, 42 and 44, extend from the insideedge of the support bar 26 towards the support bar 28. The lead 42extends perpendicularly to the bar 26 while the leads 40 and 44 curvetowards each other. The end of the lead 44 comprises the pad 38 forsupporting the chip 46 of the semiconductor device. The ends of theleads 32, 34, 36, 40 and 42 are connected by connecting wires 48 tobonding pads on the chip 46. The pg,6 chip itself is bonded to thesupport 38 whereby the lead 44 is connected to the chip 46. The innerpart of the leads 32, 34, 36, 40, 42 and 44, the pad 38, the chip 46 andthe connections 48, are all to be encapsulated by encapsulating materialwhose outline takes the shape of the rectangle 50 and whose shape may beseen in FIG. 3. Then, after encapsulation, the support bars 26 and 28are cut along the edges of the leads 32, 34, 36, 40, 42 and 44 as forexample on the dotted lines 52. In the molding step, the notch 30 actsas a gate for the entry of the encapsulating fluid into the mold cavitythat contains the inner ends of the leads 32, 34, 36, 40, 42 and 44, thechip 46 and the corresponding connections 48, the support bar 28 actingas at least a portion of one wall of the main leader as is explainedhereinafter.

The mold itself, see FIGS. 1 and 2, comprises an upper mold portion 60and a lower mold portion 62. The upper mold portion runs lengthwise ofthe strip 10 and has as many cavities 64 and 68 as are convenient, onefor each lead frame 12, the cavities 64 being large enough to includethe chip 46, the connections 48 and the inner ends of the leads 32, 34,36, 40, 42 and 44 up to the support strips 26 and 28 in one directionand up to the adjacent crossbars 24 in the other direction. The uppermold also includes a main runner 66 which runs the length thereof. Themain runner 66 is so positioned with respect to the bar 28 that the bar28 closes off at least a portion of the bottom of the runner 66 and thenotches 30 act as gates for the several cavities 64 wherebyencapsulating fluid forced down the runner 66 gets into the cavities 64and 68 by way of the notches 30. The bottom part of the mold 62 has acooperating cavity 68 that registers with the cavity 64. Due to thecontacting of the mold portions 60 and 62 on the upper and lowersurfaces of the bars 24, 26 and 24 and 28, the encapsulating fluid isretained therebetween. After the fluid has hardened in the closed mold,the mold portions 60 and 62 are removed, the end bars 14 and 16 are cutaway. The bars 26 and 28 are cut through between the several leads as onthe lines 52 and the completed encapsulated semiconductor device of FIG.3 results. The scale of the drawing is very large. Actually, thedistance between the extreme ends of the leads 32 and 34 may be about aninch, in one practical semiconductor device, and the other dimensionsmay be proportional thereto.

It is clear that two or more notches such as notch 30 may be formedalong the length of the bar 28 and between the leads 32, 34 and 36 orbetween the leads 34 and 36 and the adjacent crossbar 24. Or, if noleads extend into the space between the bars 28 and 26 from the bar 28,the notch 30 may be made any size up to the width of the completeddevice of FIG. 3, that is, the notch may extend any part or all of thedistance between the adjacent crossbars 26.

The above description is of one embodiment of this invention and thisinvention is not to be limited by the shape of the lead frame or of thechip or of the connection of the chip to the conductors comprising thelead frame but is limited only by the appended claims.

What is claimed is:
 1. In a gateless mold having a plurality of cavitiestherein, each for reception of an electrical unit attached to a framemember in order that such unit can be plastic encapsulated in saidcavities, said mold having a runner groove adjacent such cavities forreceiving liquid plastic that is introduced under pressure into saidmold and into said cavities from the runner groove in a controlledmanner through a gate opening of a predetermined size, said mold itselfhaving no such gate opening of a predetermined size extending from saidrunner groove to each said cavity to provide for such introduction ofplastic under pressure into each cavity, said gateless mold comprisingat least two parts to be closed together for a molding operation andbeing adapted to have a frame member having gates therein positionedbetween said two parts when the mold is closed for a molding operationwith said frame member adapted to fit over the mold runner groove andeach cavity in a position such that the flow of liquid plastic passesfrom said runner groove to said cavities through said frame membergates.
 2. In a mold structure having a plurality of cavities therein forencapsulating electrical devices in said cavities by means of liquidplastic under pressure which requires a gate for control of the liquidplastic introduced into each said cavity, said mold structure having arunner system therein spaced from said plurality of cavities to which tosupply plastic under pressure into each cavity, and said mold structurehaving no gate in the structure for the control of plastic introducedfrom said runner system to each of said cavities, said mold structurehaving two parts adapted to accommodate a metal body therebetween whichhas gates therein corresponding in number to said cavities in the moldstructure and said metal body being combined with said electricaldevices to be encapsulated, with said mold structure adapted toaccommodate such a metal body in a position relative to said runnersystem and a cavity when said two parts of said mold structure areclosed such that liquid plastic introduced under pressure into the moldstructure and said runner system passes from said runner system throughsaid gates and into said corresponding cavities.
 3. In a mold structureas defined in claim 2 wherein said runner system in said mold structureincludes a main runner which extends over the length thereof and iscovered by a portion of such a metal body so that the gates in thelatter control the flow of liquid plastic in the main runner to saidcorresponding cavities.
 4. In a gateless mold structure for a moldingoperation with liquid plastic under pressure having a plurality ofcavities to plastic encapsulate electrical means in each such cavity andwhich molding operation requires a gate to control the flow of liquidplastic into each cavity, said mold structure having at least two partswhich when closed for a molding operating provide said plurality ofcavities, and said mold structure including a runner groove therein forthe feeding of liquid plastic to said cavities, which said runner groovehas no gate therefrom to said plurality of cavities, and with saidtwo-part mold adapted to have a frame member introduced therein forcooperating with said electrical means to be encapsulated, which is notphysically a part of the mold structure itself, said frame member havinggates therein which are each of a predetermined size adapted to bepositioned with respect to said runner groove and said cavities so as tocontrol plastic flow through the gates to the corresponding cavities.